Abstract:

We present a simple one-pot co-assembly method for the synthesis of hierarchically structured pigment particles consisting of silica inverse-opal bricks that are doped with plasmonic absorbers. We study the interplay between the plasmonic and photonic resonances and their effect on the visual appearance of macroscopic collections of photonic bricks that are distributed in randomized orientations. Manipulating the pore geometry tunes the wavelength- and angle-dependence of the scattering profile, which can be engineered to produce angle-dependent Bragg resonances that can either enhance or contrast with the color produced by the plasmonic absorber. By controlling the overall dimensions of the photonic bricks and their aspect ratios, their preferential alignment can either be encouraged or suppressed. This causes the Bragg resonance to appear either as uniform color travel in the former case or as sparse iridescent sparkle in the latter case. By manipulating the surface chemistry of these photonic bricks, which introduces a fourth length-scale (molecular) of independent tuning into our design, we can further engineer interactions between liquids and the pores. This allows the structural color to be maintained in oil-based formulations, and enables the creation of dynamic liquid-responsive images from the pigment.

Notes:

We thank Dr. Caitlin Howell, Derek Cranshaw and Charlie Payne for helpful discussions. The work was supported by the US AFOSR under award number FA9550-09-1-0669-DOD35CAP and in part by the BASF SE. Template microfabrication and electron microscopy of the photonic bricks were performed at the Center for Nanoscale Systems (CNS) at Harvard University, a member of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the NSF under award number ECS-0335765. M.K. acknowledges support from a Feodor Lynen postdoctoral research fellowship from the Alexander von Humboldt Foundation. I.B.B. acknowledges support from a Banting Postdoctoral Fellowship funded by the Natural Sciences and Engineering Research Council of Canada (NSERC). K.R.P. acknowledges support from a DoD National Defense Science and Engineering Graduate Fellowship. N.V. acknowledges support from the Leopoldina Fellowship. T.S. acknowledges support from the Weizmann Institute of Science – National Postdoctoral Award Program for Advancing Women in Science.

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